 /* crypto/bn/bn_recp.c */

 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)

 * All rights reserved.

 *

 * This package is an SSL implementation written

 * by Eric Young (eay@cryptsoft.com).

 * The implementation was written so as to conform with Netscapes SSL.

 * 

 * This library is free for commercial and non-commercial use as CrLONG32 as

 * the following conditions are aheared to.  The following conditions

 * apply to all code found in this distribution, be it the RC4, RSA,

 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation

 * included with this distribution is covered by the same copyright terms

 * except that the holder is Tim Hudson (tjh@cryptsoft.com).

 * 

 * Copyright remains Eric Young's, and as such any Copyright notices in

 * the code are not to be removed.

 * If this package is used in a product, Eric Young should be given attribution

 * as the author of the parts of the library used.

 * This can be in the form of a textual message at program startup or

 * in documentation (online or textual) provided with the package.

 * 

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. All advertising materials mentioning features or use of this software

 *    must display the following acknowledgement:

 *    "This product includes cryptographic software written by

 *     Eric Young (eay@cryptsoft.com)"

 *    The word 'cryptographic' can be left out if the rouines from the library

 *    being used are not cryptographic related :-).

 * 4. If you include any Windows specific code (or a derivative thereof) from 

 *    the apps directory (application code) you must include an acknowledgement:

 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"

 * 

 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 * 

 * The licence and distribution terms for any publically available version or

 * derivative of this code cannot be changed.  i.e. this code cannot simply be

 * copied and put under another distribution licence

 * [including the GNU Public Licence.]

 */



#include "crypto/CrBNConfig.h"

#ifdef _BN_RECP_C



//#include <stdio.h> // for NULL

#include "crypto/CrBN.h"

#include "crypto/CrBNLcl.h"





CrINT32 BN_mod_mul_reciprocal(

BIGNUM *r,

BIGNUM *x,

BIGNUM *y,

BIGNUM *m,

BIGNUM *i,

CrINT32 nb,

BN_CTX *ctx)

	{

	CrINT32 ret=0,j;

	BIGNUM *a,*b,*c,*d;



	a=ctx->bn[ctx->tos++];

	b=ctx->bn[ctx->tos++];

	c=ctx->bn[ctx->tos++];

	d=ctx->bn[ctx->tos++];



	if (x == y)

		{ if (!BN_sqr(a,x,ctx)) goto err; }

	else

		{ if (!BN_mul(a,x,y)) goto err; }

	if (!BN_rshift(d,a,nb)) goto err;

	if (!BN_mul(b,d,i)) goto err;

	if (!BN_rshift(c,b,nb)) goto err;

	if (!BN_mul(b,m,c)) goto err;

	if (!BN_sub(r,a,b)) goto err;

	j=0;

	while (BN_cmp(r,m) >= 0)

		{

		if (j++ > 2)

			{

#ifndef NO_SSLEAY_ERROR

			BNerr(BN_F_BN_MOD_MUL_RECIPROCAL,BN_R_BAD_RECIPROCAL);

#endif

			goto err;

			}

		if (!BN_sub(r,r,m)) goto err;

		}



	ret=1;

err:

	ctx->tos-=4;

	return(ret);

	}



CrINT32 BN_reciprocal(

BIGNUM *r,

BIGNUM *m,

BN_CTX *ctx)

	{

	CrINT32 nm,ret= -1;

	BIGNUM *t;



	t=ctx->bn[ctx->tos++];



	nm=BN_num_bits(m);

	if (!BN_lshift(t,BN_value_one(),nm*2)) goto err;



	if (!BN_div(r,NULL,t,m,ctx)) goto err;

	ret=nm;

err:

	ctx->tos--;

	return(ret);

	}



#endif //end of #ifdef _BN_RECP_C



